1. Field of the Invention
This invention relates to a method of regenerating a supported-nickel hydrogenation catalyst used as a finishing catalyst in the conversion of butynediol to butanediol.
2. Description of the Prior Art
In the production of butanediol from butynediol by hydrogenation, butynediol is catalytically hydrogenated to crude butanediol. Then, in a finishing stage, the crude butanediol, which contains a minor amount of partially hydrogenated compounds, including intermediate carbonyl compounds, is again subjected to another catalytic hydrogenation to convert these intermediates to butanediol. The finishing stage is described in detail in U.S. Pat. Nos. 3,950,441; 3,449,445; 3,479,411; and 3,759,845. The result of the multi-stage process is very pure butanediol.
The final stage usually is carried out in a high pressure reactor which is filled with a fixed bed of a supported-nickel catalyst. This catalyst typically comprises about 5 to 50% by weight nickel, and, optionally, one or more promotor metals, such as copper, manganese or molybdenum, usually in an amount of about 1 to 15% by weight of the catalyst. The support is a stable, high-surface-area material, such as alumina or silica. The preferred finishing catalysts for this purpose comprises about 12 to 20% nickel, 1 to 10% copper and 0 to 1.5% manganese.
Upon extended use in the finishing hydrogenation step, the catalyst partly loses its ability to reduce the carbonyl intermediates and other impurities present in the crude butanediol. Generally deactivation of catalyst occurs after processing about 0.5-2.0 thousand pounds of butanediol per pound of catalyst. Thereupon the carbonyl number of the final butanediol product increases, and fresh catalyst must be substituted for deactivated catalyst.
The prior art suggests several alternative methods for regenerating catalysts which have lost activity. However, none of these methods are suitable for use in this system. For example, in U.S. Pat. No. 3,948,991, there is described a sequential method for the removal of a carbonaceous deposit from a deactivated Sn catalyst used in an aldol condensation. The method involves contacting the Sn catalyst in sequence with a carbonyl compound at an elevated temperature and with hydrogen at a higher temperature.
In U.S. Pat. No. 4,098,833, catalysts comprising a metal halide and a Bronsted acid containing fluorine which became deactivated by formation of allyl and alkylaromatic carbonium ion complexes are regenerated with hydrogen at 0.degree. C. to 150.degree. C.
Similarly, in U.S. Pat. No. 3,966,636, a 3-step method is disclosed for regeneration of Rh and Ru catalysts, used for hydrogenation of a carbon to carbon unsaturated bond. The sequence is hydrogenation followed by oxidation followed by hydrogenation. However, oxidation could damage the supported-nickel catalyst of this invention and could lead to local overheating due to its high exotherm.
In U.S. Pat. No. 3,670,041, olefinic unsaturated impurities present in a Pd catalyst from an aromatic-hydrocarbon-deactivated feed are selectively hydrogenated by contact with hydrogenated naphthalene and hydrogen. However, the presence of hydrogenated naphthalene would introduce impurities into the system of this invention.
As seen, for one or more reasons, the prior art methods are not suitable for supported-nickel catalysts used for second stage hydrogenation of crude butanediol. In particular, such catalysts lose activity due to the formation of carbonaceous polymers which are unreactive materials. Nickel catalysts which are supported on a porous support in a fixed bed are quite susceptible to localized heating effects on oxidation, leading to damage to the metal itself.
Accordingly, it is an object of this invention to provide a novel and useful method for regenerating the activity of a deactivated supported nickel catalyst that has lost activity due to the formation of carbonaceous polymers on its catalytic surfaces.
A further object of this invention is to provide a method of restoring substantially all the activity of a deactivated supported-nickel hydrogenation catalyst in situ in a fixed bed.
Another object herein is to provide an efficient, one-step flow process for regenerating a supported-nickel hydrogenation catalyst.
These and other objects and features of the invention will be made apparent from the following description thereof.